385 lines
14 KiB
C
385 lines
14 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _KERNEL_PRINTK_RINGBUFFER_H
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#define _KERNEL_PRINTK_RINGBUFFER_H
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#include <linux/atomic.h>
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#include <linux/dev_printk.h>
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/*
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* Meta information about each stored message.
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*
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* All fields are set by the printk code except for @seq, which is
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* set by the ringbuffer code.
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*/
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struct printk_info {
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u64 seq; /* sequence number */
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u64 ts_nsec; /* timestamp in nanoseconds */
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u16 text_len; /* length of text message */
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u8 facility; /* syslog facility */
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u8 flags:5; /* internal record flags */
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u8 level:3; /* syslog level */
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u32 caller_id; /* thread id or processor id */
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struct dev_printk_info dev_info;
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};
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/*
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* A structure providing the buffers, used by writers and readers.
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*
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* Writers:
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* Using prb_rec_init_wr(), a writer sets @text_buf_size before calling
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* prb_reserve(). On success, prb_reserve() sets @info and @text_buf to
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* buffers reserved for that writer.
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*
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* Readers:
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* Using prb_rec_init_rd(), a reader sets all fields before calling
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* prb_read_valid(). Note that the reader provides the @info and @text_buf,
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* buffers. On success, the struct pointed to by @info will be filled and
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* the char array pointed to by @text_buf will be filled with text data.
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*/
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struct printk_record {
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struct printk_info *info;
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char *text_buf;
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unsigned int text_buf_size;
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};
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/* Specifies the logical position and span of a data block. */
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struct prb_data_blk_lpos {
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unsigned long begin;
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unsigned long next;
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};
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/*
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* A descriptor: the complete meta-data for a record.
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*
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* @state_var: A bitwise combination of descriptor ID and descriptor state.
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*/
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struct prb_desc {
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atomic_long_t state_var;
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struct prb_data_blk_lpos text_blk_lpos;
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};
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/* A ringbuffer of "ID + data" elements. */
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struct prb_data_ring {
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unsigned int size_bits;
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char *data;
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atomic_long_t head_lpos;
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atomic_long_t tail_lpos;
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};
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/* A ringbuffer of "struct prb_desc" elements. */
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struct prb_desc_ring {
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unsigned int count_bits;
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struct prb_desc *descs;
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struct printk_info *infos;
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atomic_long_t head_id;
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atomic_long_t tail_id;
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atomic_long_t last_finalized_id;
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};
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/*
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* The high level structure representing the printk ringbuffer.
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*
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* @fail: Count of failed prb_reserve() calls where not even a data-less
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* record was created.
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*/
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struct printk_ringbuffer {
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struct prb_desc_ring desc_ring;
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struct prb_data_ring text_data_ring;
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atomic_long_t fail;
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};
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/*
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* Used by writers as a reserve/commit handle.
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*
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* @rb: Ringbuffer where the entry is reserved.
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* @irqflags: Saved irq flags to restore on entry commit.
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* @id: ID of the reserved descriptor.
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* @text_space: Total occupied buffer space in the text data ring, including
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* ID, alignment padding, and wrapping data blocks.
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*
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* This structure is an opaque handle for writers. Its contents are only
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* to be used by the ringbuffer implementation.
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*/
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struct prb_reserved_entry {
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struct printk_ringbuffer *rb;
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unsigned long irqflags;
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unsigned long id;
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unsigned int text_space;
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};
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/* The possible responses of a descriptor state-query. */
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enum desc_state {
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desc_miss = -1, /* ID mismatch (pseudo state) */
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desc_reserved = 0x0, /* reserved, in use by writer */
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desc_committed = 0x1, /* committed by writer, could get reopened */
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desc_finalized = 0x2, /* committed, no further modification allowed */
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desc_reusable = 0x3, /* free, not yet used by any writer */
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};
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#define _DATA_SIZE(sz_bits) (1UL << (sz_bits))
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#define _DESCS_COUNT(ct_bits) (1U << (ct_bits))
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#define DESC_SV_BITS (sizeof(unsigned long) * 8)
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#define DESC_FLAGS_SHIFT (DESC_SV_BITS - 2)
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#define DESC_FLAGS_MASK (3UL << DESC_FLAGS_SHIFT)
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#define DESC_STATE(sv) (3UL & (sv >> DESC_FLAGS_SHIFT))
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#define DESC_SV(id, state) (((unsigned long)state << DESC_FLAGS_SHIFT) | id)
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#define DESC_ID_MASK (~DESC_FLAGS_MASK)
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#define DESC_ID(sv) ((sv) & DESC_ID_MASK)
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#define FAILED_LPOS 0x1
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#define NO_LPOS 0x3
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#define FAILED_BLK_LPOS \
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{ \
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.begin = FAILED_LPOS, \
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.next = FAILED_LPOS, \
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}
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/*
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* Descriptor Bootstrap
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*
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* The descriptor array is minimally initialized to allow immediate usage
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* by readers and writers. The requirements that the descriptor array
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* initialization must satisfy:
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*
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* Req1
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* The tail must point to an existing (committed or reusable) descriptor.
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* This is required by the implementation of prb_first_seq().
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*
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* Req2
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* Readers must see that the ringbuffer is initially empty.
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*
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* Req3
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* The first record reserved by a writer is assigned sequence number 0.
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*
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* To satisfy Req1, the tail initially points to a descriptor that is
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* minimally initialized (having no data block, i.e. data-less with the
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* data block's lpos @begin and @next values set to FAILED_LPOS).
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*
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* To satisfy Req2, the initial tail descriptor is initialized to the
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* reusable state. Readers recognize reusable descriptors as existing
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* records, but skip over them.
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*
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* To satisfy Req3, the last descriptor in the array is used as the initial
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* head (and tail) descriptor. This allows the first record reserved by a
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* writer (head + 1) to be the first descriptor in the array. (Only the first
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* descriptor in the array could have a valid sequence number of 0.)
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*
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* The first time a descriptor is reserved, it is assigned a sequence number
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* with the value of the array index. A "first time reserved" descriptor can
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* be recognized because it has a sequence number of 0 but does not have an
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* index of 0. (Only the first descriptor in the array could have a valid
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* sequence number of 0.) After the first reservation, all future reservations
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* (recycling) simply involve incrementing the sequence number by the array
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* count.
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*
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* Hack #1
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* Only the first descriptor in the array is allowed to have the sequence
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* number 0. In this case it is not possible to recognize if it is being
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* reserved the first time (set to index value) or has been reserved
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* previously (increment by the array count). This is handled by _always_
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* incrementing the sequence number by the array count when reserving the
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* first descriptor in the array. In order to satisfy Req3, the sequence
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* number of the first descriptor in the array is initialized to minus
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* the array count. Then, upon the first reservation, it is incremented
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* to 0, thus satisfying Req3.
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*
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* Hack #2
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* prb_first_seq() can be called at any time by readers to retrieve the
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* sequence number of the tail descriptor. However, due to Req2 and Req3,
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* initially there are no records to report the sequence number of
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* (sequence numbers are u64 and there is nothing less than 0). To handle
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* this, the sequence number of the initial tail descriptor is initialized
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* to 0. Technically this is incorrect, because there is no record with
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* sequence number 0 (yet) and the tail descriptor is not the first
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* descriptor in the array. But it allows prb_read_valid() to correctly
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* report the existence of a record for _any_ given sequence number at all
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* times. Bootstrapping is complete when the tail is pushed the first
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* time, thus finally pointing to the first descriptor reserved by a
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* writer, which has the assigned sequence number 0.
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*/
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/*
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* Initiating Logical Value Overflows
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*
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* Both logical position (lpos) and ID values can be mapped to array indexes
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* but may experience overflows during the lifetime of the system. To ensure
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* that printk_ringbuffer can handle the overflows for these types, initial
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* values are chosen that map to the correct initial array indexes, but will
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* result in overflows soon.
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*
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* BLK0_LPOS
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* The initial @head_lpos and @tail_lpos for data rings. It is at index
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* 0 and the lpos value is such that it will overflow on the first wrap.
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*
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* DESC0_ID
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* The initial @head_id and @tail_id for the desc ring. It is at the last
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* index of the descriptor array (see Req3 above) and the ID value is such
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* that it will overflow on the second wrap.
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*/
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#define BLK0_LPOS(sz_bits) (-(_DATA_SIZE(sz_bits)))
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#define DESC0_ID(ct_bits) DESC_ID(-(_DESCS_COUNT(ct_bits) + 1))
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#define DESC0_SV(ct_bits) DESC_SV(DESC0_ID(ct_bits), desc_reusable)
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/*
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* Define a ringbuffer with an external text data buffer. The same as
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* DEFINE_PRINTKRB() but requires specifying an external buffer for the
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* text data.
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*
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* Note: The specified external buffer must be of the size:
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* 2 ^ (descbits + avgtextbits)
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*/
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#define _DEFINE_PRINTKRB(name, descbits, avgtextbits, text_buf) \
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static struct prb_desc _##name##_descs[_DESCS_COUNT(descbits)] = { \
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/* the initial head and tail */ \
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[_DESCS_COUNT(descbits) - 1] = { \
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/* reusable */ \
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.state_var = ATOMIC_INIT(DESC0_SV(descbits)), \
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/* no associated data block */ \
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.text_blk_lpos = FAILED_BLK_LPOS, \
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}, \
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}; \
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static struct printk_info _##name##_infos[_DESCS_COUNT(descbits)] = { \
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/* this will be the first record reserved by a writer */ \
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[0] = { \
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/* will be incremented to 0 on the first reservation */ \
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.seq = -(u64)_DESCS_COUNT(descbits), \
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}, \
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/* the initial head and tail */ \
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[_DESCS_COUNT(descbits) - 1] = { \
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/* reports the first seq value during the bootstrap phase */ \
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.seq = 0, \
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}, \
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}; \
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static struct printk_ringbuffer name = { \
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.desc_ring = { \
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.count_bits = descbits, \
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.descs = &_##name##_descs[0], \
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.infos = &_##name##_infos[0], \
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.head_id = ATOMIC_INIT(DESC0_ID(descbits)), \
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.tail_id = ATOMIC_INIT(DESC0_ID(descbits)), \
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.last_finalized_id = ATOMIC_INIT(DESC0_ID(descbits)), \
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}, \
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.text_data_ring = { \
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.size_bits = (avgtextbits) + (descbits), \
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.data = text_buf, \
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.head_lpos = ATOMIC_LONG_INIT(BLK0_LPOS((avgtextbits) + (descbits))), \
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.tail_lpos = ATOMIC_LONG_INIT(BLK0_LPOS((avgtextbits) + (descbits))), \
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}, \
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.fail = ATOMIC_LONG_INIT(0), \
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}
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/**
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* DEFINE_PRINTKRB() - Define a ringbuffer.
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*
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* @name: The name of the ringbuffer variable.
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* @descbits: The number of descriptors as a power-of-2 value.
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* @avgtextbits: The average text data size per record as a power-of-2 value.
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*
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* This is a macro for defining a ringbuffer and all internal structures
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* such that it is ready for immediate use. See _DEFINE_PRINTKRB() for a
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* variant where the text data buffer can be specified externally.
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*/
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#define DEFINE_PRINTKRB(name, descbits, avgtextbits) \
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static char _##name##_text[1U << ((avgtextbits) + (descbits))] \
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__aligned(__alignof__(unsigned long)); \
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_DEFINE_PRINTKRB(name, descbits, avgtextbits, &_##name##_text[0])
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/* Writer Interface */
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/**
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* prb_rec_init_wr() - Initialize a buffer for writing records.
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*
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* @r: The record to initialize.
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* @text_buf_size: The needed text buffer size.
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*/
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static inline void prb_rec_init_wr(struct printk_record *r,
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unsigned int text_buf_size)
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{
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r->info = NULL;
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r->text_buf = NULL;
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r->text_buf_size = text_buf_size;
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}
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bool prb_reserve(struct prb_reserved_entry *e, struct printk_ringbuffer *rb,
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struct printk_record *r);
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bool prb_reserve_in_last(struct prb_reserved_entry *e, struct printk_ringbuffer *rb,
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struct printk_record *r, u32 caller_id, unsigned int max_size);
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void prb_commit(struct prb_reserved_entry *e);
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void prb_final_commit(struct prb_reserved_entry *e);
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void prb_init(struct printk_ringbuffer *rb,
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char *text_buf, unsigned int text_buf_size,
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struct prb_desc *descs, unsigned int descs_count_bits,
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struct printk_info *infos);
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unsigned int prb_record_text_space(struct prb_reserved_entry *e);
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/* Reader Interface */
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/**
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* prb_rec_init_rd() - Initialize a buffer for reading records.
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*
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* @r: The record to initialize.
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* @info: A buffer to store record meta-data.
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* @text_buf: A buffer to store text data.
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* @text_buf_size: The size of @text_buf.
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*
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* Initialize all the fields that a reader is interested in. All arguments
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* (except @r) are optional. Only record data for arguments that are
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* non-NULL or non-zero will be read.
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*/
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static inline void prb_rec_init_rd(struct printk_record *r,
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struct printk_info *info,
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char *text_buf, unsigned int text_buf_size)
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{
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r->info = info;
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r->text_buf = text_buf;
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r->text_buf_size = text_buf_size;
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}
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/**
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* prb_for_each_record() - Iterate over the records of a ringbuffer.
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*
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* @from: The sequence number to begin with.
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* @rb: The ringbuffer to iterate over.
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* @s: A u64 to store the sequence number on each iteration.
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* @r: A printk_record to store the record on each iteration.
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*
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* This is a macro for conveniently iterating over a ringbuffer.
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* Note that @s may not be the sequence number of the record on each
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* iteration. For the sequence number, @r->info->seq should be checked.
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*
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* Context: Any context.
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*/
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#define prb_for_each_record(from, rb, s, r) \
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for ((s) = from; prb_read_valid(rb, s, r); (s) = (r)->info->seq + 1)
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/**
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* prb_for_each_info() - Iterate over the meta data of a ringbuffer.
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*
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* @from: The sequence number to begin with.
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* @rb: The ringbuffer to iterate over.
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* @s: A u64 to store the sequence number on each iteration.
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* @i: A printk_info to store the record meta data on each iteration.
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* @lc: An unsigned int to store the text line count of each record.
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*
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* This is a macro for conveniently iterating over a ringbuffer.
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* Note that @s may not be the sequence number of the record on each
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* iteration. For the sequence number, @r->info->seq should be checked.
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*
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* Context: Any context.
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*/
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#define prb_for_each_info(from, rb, s, i, lc) \
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for ((s) = from; prb_read_valid_info(rb, s, i, lc); (s) = (i)->seq + 1)
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bool prb_read_valid(struct printk_ringbuffer *rb, u64 seq,
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struct printk_record *r);
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bool prb_read_valid_info(struct printk_ringbuffer *rb, u64 seq,
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struct printk_info *info, unsigned int *line_count);
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u64 prb_first_valid_seq(struct printk_ringbuffer *rb);
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u64 prb_next_seq(struct printk_ringbuffer *rb);
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#endif /* _KERNEL_PRINTK_RINGBUFFER_H */
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